Comstock/Thinkstock(MANCHESTER, N.H.) -- Authorities are combing through a million-dollar New Hampshire mansion for clues to determine who brutally assaulted a local doctor and his wife before leaving them for dead last week.

Police responded to the home of Dr. Eduardo Quesada, 52, and his wife Sonia after they were attacked Saturday night in an apparent home invasion.

Police investigators, assisted by the FBI and the Drug Enforcement Administration, have said that the house is still an active crime scene as they dust for fingerprints and search for any evidence to explain what happened in the $1.4 million suburban Manchester home.

"The homeowners were obviously confronted by a person or persons of interest," Chief John Bryfonski of the Bedford police said.

There have been no arrests but police say they are seeking a person of interest. Investigators also say they have some leads, but none specific enough at this point to be helpful. They are waiting to do more intensive interviews with the couple.

Meanwhile, Dr. Quesada, a respected anesthesiologist at the Elliot Hospital Pain Management Center in Manchester, clings to life in the same facility where he works.

Police say the couple were attacked Saturday night in the home, which was up for sale. Quesada's wife was able to escape during the attack. Covered in blood, she knocked on the door of a neighbor's house, where police found her shortly after someone called 911.

"It could have potentially been a hostage situation," Bryfonski said. "That was a consideration, that was part of the plan, but the overarching concern was the safety of the homeowner and the child."

Police who stormed the house found the couple's 2-year-old child unharmed, and no sign of intruders. Dr. Quesada, however, was so battered that police said they thought he was dead.

Police have not released details of his injuries or what caused them. His wife is still in the hospital but the extent of her injuries is unclear.

"The focus of this case was the couple and maybe, in particular, the doctor and they went there with intention to perhaps steal something but perhaps harm the doctor," Brad Garrett, a former FBI agent and ABC News consultant, said.

Dr. Quesada was reportedly arrested at the house last year after a domestic disturbance call. The charges were reportedly dropped, and police won't say whether the two incidents are related.

Authorities will not say whether the family was targeted, or whether anything was stolen.